Process of forming screens



Patented Nov. 12, 1940 UNITED STATES PATENT OFFICE PROCESS OF FORMING SCREENS Willem van de Pol, Arnhem, Netherlands No Drawing. Application June 12, 1939, Serial No. 278,762. In the Netherlands October 29,

. 5 Claims.

Metal plates are known, the surface of which is provided, for instance by process engraving, with a great number of regularly spaced, small recesses filled, by mechanical means, with as- 5 phalt or another electrically insulating substance.

Such a plateis adapted for use as a matrix or backing for making screens or sieves. To this end,the plate is immersed in a galvanic bath and provided therein with a metaldeposit in the form of a screen. However, the use of these matrices for the purpose stated meets with the inconvenience that, when the metal deposit is removed therefrom, a more or less considerable number of insulating grains or dots are pulled out of the matrix, thus necessitating a tedious and expensive repair thereof.

My present invention has for its object to obviate this inconvenience and it consists in using, as a matrix for making screens or the like, a metal plate whose surface is provided with insulating grains of the oxide, the hydroxide or an-,

other suitable compound of the same or of another metal. Very suitable ior the purpose is a plate of aluminium or an aluminium alloy, which is locally oxidized, chemically or anodically. Other suitable metals are magnesium provided with a deposit of magnesium oxide--copper having a deposit of aluminium oxide-or the magnesium-aluminium alloy known as magnaliurn and adapted to be anodically oxidized. Should the grains, which are good insulators in dry condition, be too porous to entirely prevent in a galvanic bath the deposit of metal on the parts covered thereby, a suitable insulating material such as wax may be embodied in the grains.

A simple and reliable process of making a matrix for the purpose under review consists herein that a plate of aluminium, or of a suitable aluminium alloy, is coated with a continuous layer of material, sensitive to light, and thereupon exposed through a. glass plate covered with a great number of regularly spaced opaque dots. Thereafter, the non-exposed, i. e. the non-hardened parts of the coating are washed away, so that saidparts of the aluminium surface are cleared. It the plate is thereupon subjected to oxidation, forinstance anodic oxidation, only those parts of the metal surface are oxidized from which the coating has been washed away. After removal of the remainder of the sensitive coatingfthe plate carries a great number of regularly spaced grains or dots of aluminiiim oxide, which very firmly adhere to the metal. In order that this oxide may have the required insulating property in the galvanic bath, in which the screens are subsequently to be deposited on the matrix, the plate may for instance be rolled up with wax or another suitable material, which thus fills up the pores of the oxide, without adhering in any appreciable amount to the bare metal of the plate.

As an alternative, the entire surface of the metal plate may be coated with oxide, whereupon the latter is removed along a series of lines running across each other at right angles. To this end, a great number of regularly spaced grains of asphalt may be deposited on the coating by photographic means well-known in the art, which grains ofl'er suflicient resistance to the action of the lye, with which the oxide is to be removed.

Foroxidizing the metal plate, either in the form of isolated grains, or in the form of an even layer, any other suitable method may be used. For instance, the metal plate may be immersed in a bath, from which a metal oxide, or a metal hydroxide, or another metal compound adapted to be converted into oxide, can be deposited upon the plate.

In order that the metal oxide or the other metal compound may very firmly adhere to the preferably polished metal plate, the bare portions of the plate may be etched before oxidation. It is even possible in this manner to provide the plate with the usual recesses, which are thereupon filled up with oxide.

The matrix thus produced may, if desired, be provided with a deposit of another metal, upon which the screens are to be formed. I In this case it is not necessary first to remove the oxide (provided that the plate has been coated with a continuous layer thereof as hereinbefore described) along a series of lines running across each other at right angles, but it suffices to provide said coating with a great number of regularly spaced insulating grains, for instance by printing ,with suitable ink, which is burnt in with powdered asphalt or resin, and thereupon to deposit said other metal around these grains.

If the metal plate, prior or after the described operation, is shaped as a cylinder, and if said cylinder, after being mounted on horizontal trunnions, is partly immersed in the galvanic bath and slowly rotated, endless screens can be removed therefrom.

If the marginal portions of the matrix are kept clear of insulating grains, the matrix can be used for making screens enclosed by a frame.

The process and the matrix in accordance with the invention are also suitable for other purposes and' can be used in all cases wherein it is desired for a substance to be electrically deposited from a bath, for instance rubber from latex or a rubber solution, in such a manner that a positive potential is applied to the plate, and a negative potential is applied to a neutral electrode in the bath. In this manner, it is possible to make rubber screens.

What I claim is:

1. The process of making a sieve comprising oxidizing selected areas of a metal matrix to provide portions composed of a firmly adherent metal oxide corresponding to the perforations of the finished sieve, incorporating a non-metallic insulating substance in said portions: of metal oxide thereby rendering said, areas resistant to electro-deposition, electro-depositing a sheet of material on said matrix and finally detaching the deposited material from said matrix. V

2. The process of making a sieve'comprising oxidizing selected areas of a metal matrix to pro vide portions composed of a firmly adherent metal oxide corresponding to the perforations of the finished sieve, incorporating a non-metallic insulating substance in said portions of metal oxide. thereby rendering said areas resistant to electro-deposition, electro-depositlng a sheet of metal on said matrix and finally detaching the deposited metal from said matrix.

3. The process of making a sieve comprising oxidizing selected areas of an aluminium matrix to provide portions composed of firmly adherent aluminium oxide corresponding to the perforations of the finished sieve, incorporating a nonmetallic insulating substance in said portions of aluminium oxide thereby rendering said areas Y resistant to electro-deposition, eleotro-depositing a sheet of material on said matrix and finally detaching the deposited material from said matrix. A

4. The process of making a sieve comprising oxidizing selected areas of an aluminium alloy matrix to provide portions composed of firmly adherent oxide of the aluminium alloy, said areas corresponding to the perforations of the finished sieve, incorporating a non-metallic insulating substance in said portions of aluminium alloy oxide thereby rendering said areas resistant to electro-deposition, electro-depositing a sheet of material on said matrix and finally detaching the deposited material from said matrix.

5. A process of making a sieve comprising oxidizing selected areas of an aluminium matrix to provide portions composed of firmly adherent aluminium oxide corresponding to the perforations 01' the finished sieve, incorporating a nonmetallic insulating substance in said portions of aluminium oxide thereby rendering said areas resistant to electro-deposition, electro-deposi-ting a sheet of metal on said matrix and finally detaching the deposited metal from said matrix.

WILLEM VAN ns POL.

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